This article presents the development of a palm-sized all-in-one 10-W peak-power, continuously frequency tunable backward terahertz (THz)-wave parametric oscillator (BW-TPO). The BW-TPO incorporates a passively Q-switched 1064-nm Nd:YAG microchip laser driving pump source, a slant-stripe-type periodically poled lithium niobate (PPLN) crystal gain medium mounted on a motorized rotation stage, a simple layout for the injection seeding to the idler wavelength, and all the necessary optical components. A maximum peak power of 15 W was obtained at 0.33 THz. Continuous tunability from 0.29 to 0.35 THz was achieved by mechanical rotation of the PPLN crystal. The BW-TPO is suitable for real-world THz-wave nondestructive sensing applications.